digit (unit)

{{main|Ancient Egyptian units of measurement}}

The digit, also called a finger or fingerbreadth, is a unit of measurement originally based on the breadth of a human finger. In Ancient Egypt it was the basic unit of subdivision of the cubit.

On surviving Ancient Egyptian cubit-rods, the royal cubit is divided into seven palms of four digits or fingers each. The royal cubit measured approximately 525 mm, so the length of the ancient Egyptian digit was about 19 mm.

{{main|Ancient Mesopotamian units of measurement}}

In the classical Akkadian Empire system instituted in about 2250 BC during the reign of Naram-Sin, the finger was one-thirtieth of a cubit length. The cubit was equivalent to approximately 497 mm, so the finger was equal to about 17 mm. Basic length was used in architecture and field division.

{{main|Ancient Hebrew units of measurement}}

{{main|Ancient Greek units of measurement}}

{{main|Ancient Roman units of measurement}}

{{main|English units}}

A digit (lat. digitus, "finger"), when used as a unit of length, is usually a sixteenth of a foot or 3/4" (1.905 cm for the international inch).{{cite book|author=Ronald Edward Zupko|authorlink=Ronald Edward Zupko|title=A dictionary of weights and measures for the British Isles: the Middle Ages to the twentieth century|url=https://archive.org/details/bub_gb_0l_k-XMIiQIC|accessdate=15 January 2012|year=1985|publisher=American Philosophical Society|isbn=978-0-87169-168-2|pages=[https://archive.org/details/bub_gb_0l_k-XMIiQIC/page/n143 109]–10}} The width of an adult human male finger tip is indeed about 2 centimetres. In English this unit has mostly fallen out of use, as do others based on the human arm: finger (7/6 digit), palm (4 digits), hand (16/3 digits), shaftment (8 digits), span (12 digits), cubit (24 digits) and ell (60 digits).

In astronomy a digit is, or was until recently, one twelfth of the diameter of the sun or the moon. This is found in the Moralia of Plutarch, XII:23, but the definition as exactly one twelfth of the diameter may be due to Ptolemy. Sosigenes of Alexandria had observed in the 1st century AD that on a dioptra, a disc with a diameter of 11 or 12 digits (of length) was needed to cover the moon.

The unit was used in Arab or Islamic astronomical works such as those of Ṣadr al‐Sharīʿa al‐Thānī (d.1346/7), where it is called {{langx|ar|إصبعا}} iṣba' , digit or finger.

The astronomical digit was in use in Britain for centuries. Heath, writing in 1760, explains that 12 digits are equal to the diameter in eclipse of the sun, but that 23 may be needed for the Earth's shadow as it eclipses the moon, those over 12 representing the extent to which the Earth's shadow is larger than the Moon. The unit is apparently not in current use, but is found in recent dictionaries.

• Finger (unit)
• Finger tip unit
• Cubit
• Anthropic units

{{reflist|refs=

{{cite EB1911|wstitle=Digit |volume=8 |page=268}}

Hosch, William L. (ed.) (2010) [https://books.google.com/books?id=cuN7rH6RzikC The Britannica Guide to Numbers and Measurement] New York, NY: Britannica Educational Publications, 1st edition. {{ISBN|978-1-61530-108-9}}, p.203

Macdonald, A.M. (ed.) (1972) Chambers Twentieth Century Dictionary Edinburgh: W. & R. Chambers {{ISBN|0-550-10206-X}}, "digit"

{{cite book|last=Clagett|first=Marshall|title=Ancient Egyptian Science, A Source Book. Volume 3: Ancient Egyptian Mathematics|year= 1999|publisher= American Philosophical Society|location= Philadelphia|isbn= 978-0-87169-232-0|url= https://archive.org/details/bub_gb_8c10QYoGa4UC}}

{{cite book |last=Heath |first=Robert |authorlink=Robert Heath (mathematician) |year=1760 |url=https://archive.org/details/astronomiaaccur00heatgoog |title=Astronomia accurata; or ... subservient to the three principal Subjects |publisher=Published by the author. |location= London |page=ix}}

Hockey, Thomas et al. (eds.) (2007) [http://islamsci.mcgill.ca/RASI/BEA/Sadr_al-Sharia_al-Thani_BEA.htm The Biographical Encyclopedia of Astronomers, Springer Reference] New York: Springer pp. 1002–1003

{{cite book|last=Lepsius|first=Richard|title=Die altaegyptische Elle und ihre Eintheilung|year=1865|publisher=Dümmler|location=Berlin|url=https://archive.org/details/bub_gb_PRQGAAAAQAAJ|language=German}}

Neugebauer, Otto (1975) [https://books.google.com/books?id=vO5FCVIxz2YC A History of Ancient Mathematical Astronomy] Berlin: Springer, {{ISBN|978-0-387-06995-1}} Volume 2, p.658

Plutarchus Chaeronensis, Frank Cole Babbitt (trans.) (1957) [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Moralia/The_Face_in_the_Moon*/C.html#ref226 Plutarch's Moralia: In fifteen volumes] London: William Heinemann, Cambridge, Mass.: Harvard University Press, Volume XII p.144

'Ubayd Allāh ibn Mas'ūd Ṣadr al-S̆arīaẗ al-Aṣġar al-Maḥbūbī, Ahmad S. Dallal (1995) [https://books.google.com/books?id=ULp2LGmKTSMC An Islamic response to Greek astronomy: kitāb Ta'dīl hay'at al-aflāk of Ṣadr al-Sharī'a] (in Arabic and English) Leiden, New York: E.J. Brill, {{ISBN|978-90-04-09968-5}} p.212

{{cite book|editor-last=Selin|editor-first=Helaine|editor-link=Helaine Selin|title=Encyclopaedia of the History of Science, Technology and Medicine in non-Western Cultures|year= 1997|publisher= Kluwer|location= Dordrecht|isbn= 978-0-7923-4066-9|url=https://books.google.com/books?id=raKRY3KQspsC}}

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{{DEFAULTSORT:Digit (Length)}}

Category:Units of length

Category:Human-based units of measurement